The formation of resist masks in the manufacture of integrated circuits using radiation sensitive layers which contain various organic polymers, such as alkali soluble resins, mixed with photosensitizers such as light sensitive diazo compounds is known. Layers of the light sensitive material are formed on a substrate, exposed to light or other activating radiation in a patternwise manner, and a visible image is developed by removing the more soluble portions of the layer with a developing solution. In order to improve the characteristics of the remaining portions of the resist layer, such as its adhesion to various substrates, or its resistance to chemical and/or thermal degradation, the pattern resist layer is conventionally baked at an elevated temperature. The thermoplastic polymer materials in the resist are subject to flow at temperatures above their second order glass transition temperatures. This tendency to flow distorts the resist pattern, and in the fine geometry patterns which are required, for example, in integrated circuit manufacture the distortion can result in dimensional changes or even the closing of fine lines. The baking, therefore, must be limited to temperatures below which flow would cause unacceptable pattern distortion.